Segmented windings are commonly used in modern electrical machine applications, such as in hybrid-electric vehicles. These windings typically comprise a plurality of segmented conductors which include in-slot portions and ends that are connected together. The conductors are positioned in the slots of a laminated core portion of the electric machine (e.g. stator slots), and the ends of the conductors are connected to form windings for the electric machine.
Segmented conductors for electric machines are often provided in the form of “U-shaped” conductors which include two legs and a central U-turn portion extending between the legs. These U-shaped conductors may also be referred to herein as “U-shaped bars” or conductors with “U-turn portions”. The terms “U-shaped conductor”, “U-shaped bar” and “U-turn portion” as used herein refer to electric conductors or conductor portions where the axial direction of the conductor changes by about 180°. However, these terms are not limited to conductors or conductor portions that form a perfect “U” shape.
U-shaped conductors are typically created by bending and twisting wire bars into U-shaped conductors with two legs and a U-turn between the legs. The two legs are separated by a given span which allows the conductor to extend across a number of stator slots by virtue of the U-turn alone. The legs of the conductors are then inserted into the slots of the core from an insertion end of the core. Following insertion of the conductors into the slots of the core, the bend portions (i.e., the U-turn portions) are positioned on one side of the core (i.e., the “insertion side”) and the leg ends extend from the other side of the core (i.e., the “connection side” or “weld side”). The legs ends may then be bent to appropriate positions, often with a first leg typically bent in one direction and another leg bent in the opposite direction such that the entire segmented extends a given slot span (e.g., 12 slots). Finally, the tips of the leg ends are connected together at the connection side of the stator to complete the windings. These connections include adjacent leg ends that are directly aligned and joined together (e.g., by welding), non-adjacent leg ends that are connected through jumper wires, and terminal connections. Together, the connected conductors form the complete winding arrangement.
Although the conductors are connected together at their ends, care must be taken to ensure that adjacent conductors do not touch each other and short-circuit the designed winding arrangement. Accordingly, a slot liner comprised of an electrical insulation material is typically provided within the slots of the stator in order to electrically insulate the conductors from the stator core. The conductor itself may also have an insulation coating that covers the conductor within and outward of the stator core.
Care must be taken when the windings are assembled on the stators to avoid electrical shorts between conductors or between a conductor and the lamination steel of the stator core. Electrical shorts between the conductors and the lamination steel often result from manufacturing imperfections in the lamination slot geometry, imperfections in the conductor, and/or inadequate slot liner insulation. In electric motor applications where a U-shaped conductor is used, the slot liner may take the form of an “S”, as shown in FIG. 10A. With this arrangement, the conductor is situated in each pocket of the “S” so that each conductor is isolated from the adjacent conductors. However, openings existing between the slot liner and the inner surface of the stator slot. These openings create a potential arc path for a short to occur if the conductor has been damaged or has manufacturing imperfections.
Another slot liner constructions that has been used is a slot liner in the form of a “B”, as shown in FIG. 10B. However this form factor requires additional layers of unnecessary slot liner paper to be used (e.g., see double layer 99 in FIG. 10B) to be used between the conductors. This additional liner layer occupies space that could have been used for an increased volume of copper needed for a high slot-fill ratio, which is desired for increased machine performance. It will also be noted that additional layers between conductors are also required with “S” shaped slot liners when four or more conductors are positioned in each slot, and each conductor must be insulated from its adjacent conductors (e.g., see double layer 99 in FIG. 10A).
Accordingly, it would be advantageous to provide an insulation arrangement for electric machines with segmented conductors which provides increased protection from electrical shorts to ground while also providing for a high slot-fill ratio. It would be advantageous if such insulation arrangement could be provided easily and at relatively low cost to the manufacturer.